In recent years, according to the rapid development of the MEMS technology, an interest on a micro thermoelectric conversion element is increasing. A normal thermoelectric conversion element, that is, the micro thermoelectric conversion element is manufactured through processes such as cutting. This is because a thermoelectric material is generally fragile and has low strength, and machining in a submillimeter order or less is therefore significantly difficult. When the machining is used, manufacturing of a curved surface and an uneven shape is difficult.
The micro thermoelectric conversion element is expected to be applied to a portable micro energy source, a local cooling device, a sensor, or the like. In particular, it is expected that the micro thermoelectric element is incorporated in a composite device for a sensor network and used as a maintenance-free power supply that uses waste heat and body temperature.
In the micro thermoelectric conversion element, since heat resistance of the element is significantly small, it is difficult to apply a large temperature difference to the thermoelectric conversion element. Therefore, it is desirable that an inter-electrode distance, that is, the thickness of the thermoelectric material can be easily adjusted as appropriate.
It is relatively easy to reduce the inter-electrode distance of the thermoelectric conversion element, that is, reduce the thickness of the thermoelectric material. However, it is considerably difficult to increase the inter-electrode distance, that is, increase the thickness of the thermoelectric material. In order to manufacture such a micro thermoelectric conversion element having a long inter-electrode distance, that is, a high aspect ratio, it is proposed to perform fine patterning of the thermoelectric material using a semiconductor process and a MEMS technique.
FIG. 12A to FIG. 12D are explanatory diagrams of a manufacturing process for the conventional micro thermoelectric conversion element. First, as illustrated in FIG. 12A, columnar holes 42 formed by fine patterns having a high aspect ratio are formed on a silicon substrate 41 by the MEMS technique to manufacture a silicon mold.
Subsequently, as illustrated in FIG. 12B, slurry including piezoelectric ceramics powder and a binder is applied to the silicon mold and a coating film 43 is formed by filling the columnar holes 42 with the slurry.
Subsequently, as illustrated in FIG. 12C, after the coating film 43 is dried, the binder is removed. Subsequently, after a sample, from which the binder is removed, is wrapped with ceramics powder for protection (not illustrated in the figure), the sample is pressurized and baked at a sintering temperature of the piezoelectric ceramics to form piezoelectric ceramics 44.
Subsequently, as illustrated in FIG. 12D, after the ceramics powder for protection is removed, the silicon mold is etched and removed and the piezoelectric ceramics 44 is extracted. Consequently, a basic configuration of the micro thermoelectric conversion element is completed.
Here, silicon that has a high melting point (1414° C.) and high hardness (Knoop hardness: 8.3 GPa) and for which fine and high-aspect patterning can be performed according to the development of the MEMS technology is used as the mold. Consequently, it is possible to form a particularly fine structural body compared with the machining.
Patent Literature 1: Japanese Patent Application Laid-Open No. H11-274592.